阅读说明：本技术 1570MPa级抗延迟断裂钢棒及其制造方法 (1570 MPa-grade delayed fracture resistant steel bar and manufacturing method thereof ) 是由 尹一 刘祥 陈克东 徐曦 安绘竹 于 2019-10-31 设计创作，主要内容包括：1570MPa级抗延迟断裂钢棒及其制造方法,钢中化学成分按重量百分比计含有：C：0.34％～0.37％,Si：1.80％～2.00％,Mn：0.60％～0.90％,P：≤0.020％,S：≤0.020％,Ti：0.05％～0.08％,余量为Fe和不可避免的杂质。与现有技术相比,本发明的有益效果是：一种1570MPa级抗延迟断裂PC钢棒用盘条及其制造方法,提高Si元素含量,合理添加金属元素Ti,并调整热轧控冷和钢棒生产工艺,主要用于高强度抗延迟断裂PC钢棒,能够满足在1570MPa强度级下抗延迟断裂的要求。(1570 MPa-level delayed fracture resistant steel bar and a manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by weight: c: 0.34-0.37%, Si: 1.80% -2.00%, Mn: 0.60% -0.90%, P: less than or equal to 0.020%, S: less than or equal to 0.020%, Ti: 0.05 to 0.08 percent, and the balance of Fe and inevitable impurities. Compared with the prior art, the invention has the beneficial effects that: a wire rod for 1570 MPa-level delayed fracture resistant PC steel rod and a manufacturing method thereof are disclosed, which improve the content of Si element, reasonably add metal element Ti, and adjust the hot rolling cooling control and steel rod production process, are mainly used for high-strength delayed fracture resistant PC steel rod, and can meet the requirement of delayed fracture resistance under 1570MPa strength level.)

The 1.1570 MPa-grade delayed fracture resistant steel bar is characterized in that the steel comprises the following chemical components in percentage by weight: c: 0.34-0.37%, Si: 1.80% -2.00%, Mn: 0.60% -0.90%, P: less than or equal to 0.020%, S: less than or equal to 0.020%, Ti: 0.05 to 0.08 percent, and the balance of Fe and inevitable impurities.

2. The method of manufacturing a 1570MPa grade delayed fracture resistant steel bar of claim 1, wherein;

1) controlling the drawing speed of the continuous casting square billet to be not more than 1.2 m/min; controlling the heating speed to be not more than 15 ℃/min and the soaking temperature to be 1150 +/-15 ℃ when the steel billet is heated;

2) the diameter of the wire rod is 12-14mm, and the spinning temperature is 890 +/-15 ℃;

3) the quenching temperature is 920-950 ℃, the tempering temperature is 430-460 ℃ and the running speed of the steel bar is 30-45m/min in the production process of the steel bar.

3. The 1570MPa grade delayed fracture resistant steel bar according to claim 1, wherein the wire rod microstructure is ferrite + pearlite, the ferrite content is 20-30% by volume, the grain size is grade 6-8, and the decarburized layer depth is less than or equal to 0.05 mm.

4. The steel wire rod for the 1570 MPa-grade delayed fracture-resistant steel rod as claimed in claim 1, wherein the tensile strength of the wire rod is 800-850MPa, and the reduction of area is not less than 45%.

Technical Field

The invention belongs to the technical field of hot-rolled wire rods, and particularly relates to a 1570 MPa-grade delayed fracture resistant steel bar and a manufacturing method thereof.

Background

The PC steel rod for the tubular pile adopts a medium-carbon low-alloy steel wire rod, and is subjected to mechanical dephosphorization, pre-drawing, spiral groove forming, induction heating to over 900 ℃ for quenching, and tempering at over 400 ℃ to obtain a tempered troostite structure. The strength grade of the steel bar is generally 1470MPa grade. In order to improve hardenability, alloy elements for improving hardenability are added to the steel. Because the induction heating speed is high in the production process of the steel bar, alloy elements and impurity elements in the steel cannot be completely dissolved in the austenitizing process and are gathered at the original austenite grain boundary, after quenching and tempering, the impurities become hydrogen gathering points at the original austenite grain boundary, and in the processes of coil storage, tension and service of the steel bar, delayed fracture is generated due to hydrogen embrittlement, so that the method is an important quality defect of the PC steel bar.

The common strength grade of the PC steel bar is 1470MPa, the common steel grade is 30MnSi, the content of C in the steel is 0.28-0.33%, the content of Si is 0.60-0.90%, the content of Mn is 0.90-1.30%, no other alloy elements exist, the strength of the steel bar can only reach 1420MPa grade, and the problem of delayed fracture often occurs. Along with the use of large-specification tubular piles in port construction, the requirement for 1570 MPa-level steel bars is provided. The steel grade of the steel bar commonly used at present is 35Si₂Mn, C content in steel is 0.34-0.38%, Si content is 1.55-1.85%, Mn content is 0.60-0.90%, and no other alloy elements exist. After the strength of the steel bar is improved, the delayed fracture sensitivity of the steel bar is improved. Due to the existing 35Si₂The Mn steel has low Si content and does not add micro-alloy elements for inhibiting delayed fracture, so that the delayed fracture problem of the steel bar is frequently caused. Therefore, the 1570MPa PC steel bar is developed, the strength of the steel bar is improved, the delayed fracture sensitivity of the steel bar is reduced, the yield ratio of the steel bar is reduced, the uniform elongation performance is improved, and the steel bar is prevented from being rapidly fractured after being yielded.

Disclosure of Invention

The invention provides a 1570 MPa-level delayed fracture resistant PC steel bar and a manufacturing method thereof, which are mainly used for a high-strength delayed fracture resistant PC steel bar and can meet the requirement of delayed fracture resistance under the 1570MPa strength level, the content of Si element is improved, the metal element Ti is reasonably added, and hot rolling cooling control and steel bar production processes are adjusted.

In order to achieve the purpose, the invention adopts the following technical scheme:

the 1570 MPa-level delayed fracture resistant steel bar comprises the following chemical components in percentage by weight: c: 0.34-0.37%, Si: 1.80% -2.00%, Mn: 0.60% -0.90%, P: less than or equal to 0.020%, S: less than or equal to 0.020%, Ti: 0.05 to 0.08 percent, and the balance of Fe and inevitable impurities.

C: the C content is increased, the hardenability of the steel and the precipitation of carbide during tempering can be improved, and the strength of the steel bar is improved. When the carbon content in the steel exceeds 0.37 wt%, the seam weldability is lowered, so the carbon content is controlled to 0.34 wt% to 0.37 wt%.

Si: the hardenability of the steel can be improved, the strength is improved through solid solution strengthening, the decomposition and transformation speed of the structure in the tempering process after the base metal is quenched can be reduced, the tempering resistance is increased, and the tempering stability of the structure is improved, so that the degree of the reduction of the strength along with the rise of the tempering temperature is weakened, the controllability of the performance of the steel bar in the production process is improved, and the higher the Si content is, the stronger the delayed fracture resistance of the steel is. But the rolling welding performance is influenced by the excessively high Si content, and the silicon content is controlled to be 1.80-2.00 wt% according to the calculation of tensile strength.

Mn combines with S to form MnS, and hydrogen-induced cracking tends to cause delayed fracture with the MnS as a starting point, which increases the delayed fracture sensitivity of high-strength steel without greatly affecting hardenability and strength, so that the Mn content is controlled to 0.6 wt% to 0.9 wt%.

P and S are harmful elements which can reduce the plasticity and toughness of the steel, so that the smaller the content, the better.

Ti: the crystal grains are refined, the segregation of elements in the crystal grain boundary is reduced, and submicron Ti compounds formed by the crystal grains and C, N are precipitated during tempering, and vanadium carbonitride precipitated during tempering is an effective hydrogen trap. The hydrogen traps distributed in a transgranular way capture absorbed hydrogen, so that the hydrogen cannot diffuse, the hydrogen concentration of the grain boundary is reduced, and the cracking of the grain boundary is prevented. Therefore, the Ti element is added to inhibit the delayed fracture tendency of the steel bar and improve the delayed fracture resistance of the steel bar.

A manufacturing method of 1570 MPa-level delayed fracture resistant steel bar,

1) controlling the drawing speed of the continuous casting square billet to be not more than 1.2 m/min; controlling the heating speed to be not more than 15 ℃/min and the soaking temperature to be 1150 +/-15 ℃ when the steel billet is heated;

2) the diameter of the wire rod is 12-14mm, and the spinning temperature is 890 +/-15 ℃;

3) the quenching temperature is 920-950 ℃, the tempering temperature is 430-460 ℃ and the running speed of the steel bar is 30-45m/min in the production process of the steel bar.

The wire rod microstructure is ferrite and pearlite, the ferrite accounts for 20-30% by volume percentage, the grain size is 6-8 grades, and the depth of a decarburized layer is less than or equal to 0.05 mm.

The tensile strength of the wire rod is 800-850MPa, and the reduction of area is more than or equal to 45 percent.

Compared with the prior art, the invention has the beneficial effects that:

1) the components of the invention consider the requirements of satisfying the tensile strength and other mechanical properties of 1570 MPa-level PC steel bar, consider the problem of the delayed fracture sensitivity rising after the tensile strength rising, reduce the segregation of crystal boundary elements by optimizing the chemical components and adding Ti element to refine crystal grains, and form hydrogen traps to capture diffusible hydrogen by the precipitation and transgranular distribution of titanium carbonitride, thereby preventing delayed fracture.

2) The invention reasonably optimizes the components of each element, ensures that the components are easy to control stably during smelting, and adjusts the rolling cooling process to obtain a product with more excellent performance. Stress corrosion performance tests on the obtained steel rod processed by the wire rod show that: the steel rod produced by the steel rod for the 1570MPa grade steel rod has higher stress corrosion performance than the steel rod produced by a common steel rod and stable mechanical property.

Drawings

FIG. 1 is a gold phase diagram (x 500) of the microstructure of the wire rod of the present invention;

FIG. 2 is a gold phase diagram (x 500) of the microstructure of the steel bar according to the invention;

FIG. 3 is a precipitation plot (x 20000) of tempered titanium carbonitride in a steel bar;

Detailed Description

The following examples are provided to further illustrate the embodiments of the present invention:

referring to the figures 1-3, the 1570MPa grade delayed fracture resistant steel bar comprises the following chemical components in percentage by weight: c: 0.34-0.37%, Si: 1.80% -2.00%, Mn: 0.60% -0.90%, P: less than or equal to 0.020%, S: less than or equal to 0.020%, Ti: 0.05 to 0.08 percent, and the balance of Fe and inevitable impurities.

A manufacturing method of 1570 MPa-level delayed fracture resistant steel bar,

1) the steel for the wire rod is smelted by a converter, LF refined and continuously cast into (178-²The steel type P, S of the square billet is low in content and high in carbon content, so that low-S molten iron is selected during smelting, slag-stopping and tapping are performed, Ar is blown from the top of the tank, and synthetic slag washing is performed, so that the molten steel is ensured to be uniform in component and low in impurity content. The liquid steel has poor fluidity and large solidification shrinkage, and the drawing speed is controlled to be not more than 1.2m/min during continuous casting; because Si-containing steel has poor thermal conductivity and is easy to crack and burn, the temperature rise speed is controlled to be not more than 15 ℃/min and the soaking temperature is controlled to be 1150 +/-15 ℃ when the billet is heated.

2) The drawing coefficient is controlled during rolling to ensure the surface quality, the water cooling and air cooling flow is controlled according to different specifications, the spinning temperature is 890 +/-15 ℃, the inlet speed of a cooling control roller way is 0.2-0.4m/s, 50% of 1-3 fans are turned on, the control cooling roller way is used for controlling the ferrite content, 4-7 fans are turned off, and the product structure performance is ensured.

3) Because the content of Si in the steel is increased, the strength is improved through solid solution strengthening, the decomposition and transformation speed of the structure in the tempering process after the quenching of the base metal is slowed down, the tempering resistance is increased, the tempering stability of the structure is improved, and the degree of the strength reduction along with the tempering temperature rise is weakened. Meanwhile, Ti is added, so that precipitation strengthening is performed during tempering, and the strength of the steel bar is improved. For the reasons, the quenching temperature is 920-950 ℃, the tempering temperature is 430-460 ℃ and the running speed of the steel bar is 30-45m/min in the production process of the steel bar. The delayed fracture tendency is reduced, the uniform extensibility of the steel bar is improved, and simultaneously the tensile strength can be ensured to meet the requirement.

The wire rod microstructure is ferrite and pearlite, the ferrite accounts for 20-30% by volume percentage, the grain size is 6-8 grades, and the depth of a decarburized layer is less than or equal to 0.05 mm.

The tensile strength of the wire rod is 800-850MPa, and the reduction of area is more than or equal to 45 percent

The following are the production processes corresponding to the respective chemical components of the examples and comparative examples of the present invention. Wherein, table 1 shows the specific component design of the comparative example and the example of the wire rod of the present invention, table 2 shows the controlled cooling process of the hot rolling production of the comparative example and the example of the wire rod of the present invention, table 3 shows the mechanical property test results of the comparative example and the example of the wire rod of the present invention, table 4 shows the production process of the steel rod of the comparative example and the example of the present invention, table 5 shows the mechanical properties of the steel rod of the comparative example and the example of the present invention, and table 6 shows the stress corrosion property test results of the comparative example and the example of the present invention.

TABLE 1 specific chemical composition (Wt%)

TABLE 2 controlled Cooling Process conditions

TABLE 3 mechanical property test results of wire rod

Table 4 steel bar production process

TABLE 5 mechanical test results of steel bars

TABLE 6 stress Corrosion test results

Aiming at the delayed fracture problem of the 1570MPa PC steel bar, the invention solves the delayed fracture problem of the high-strength steel bar and improves the uniform elongation performance by improving the chemical composition design of the wire rod for the steel bar and increasing the tempering temperature in the production process of the steel bar. By analyzing the reason of delayed fracture of the high-strength PC steel bar, the influence of each element on the delayed fracture sensitivity of the steel bar and the effects of alloy elements on strengthening original austenite grain boundary and reducing delayed fracture sensitivity, the medium-carbon high-silicon manganese steel is determined to be adopted, the Si content is increased, the tempering temperature in steel bar production is increased by adding Ti element, the tensile strength of the PC steel bar is ensured, the delayed fracture resistance is improved, and a coil rod for 1570MPa grade delayed fracture resistant PC steel bar which can be popularized and used is researched and developed. The invention is based on solving the problem of delayed fracture of the high-strength PC steel bar, is applied to the industries of steel bars and pipe piles for prestressed concrete, has excellent mechanical property, delayed fracture resistance and economy, and has wide market prospect.